Analysis of the alloy elements in antique coins

When researching the origin of antique coins, scientists use a variety of information sources. The smelting process or the ores used in minting for example contain information about the origin or the age of the coin. However, one needs to find ways to retrieve this information out of these often precious and rare coins without damaging them. But because coin alloys always contain both light and heavy elements, to gain meaningful results the researchers need a determination method that covers a wide range of elements and employs an efficient measurement routine.

A suitable way of learning more about the smelting process or the ores used in minting is x-ray fluorescence analysis (XRF). One of the biggest advantages of XRF is its non-destructive principle, keeping the sample intact while still allowing to analyse the composition at discretionary positions.

As an example, we analysed the composition of a Roman coin from 355 AD bearing the likeness of Constantine II. The results of a measurement using the FISCHERSCOPE® X-RAY XUV® are shown in Table 1: 13 elements are present in the alloy, including very light ones such as aluminium and silicon as well as heavy ones such as silver and lead.

Fig.1: Roman coin made in Constantinople in approximately 355 AD; found in Saarland in 2005. The rectangle marks the analysed area.

The evaluation software WinFTM®, with which all FISCHERSCOPE® X-RAY instruments are equipped, includes a very powerful routine that automatically employs multiple excitation conditions (x-ray tube voltage or primary filter), enabling optimal simultaneous detection of both light and heavy elements on any given sample – in one measurement step.

Element

content [%]

Element

content [%]

Al

2.52 ± 0.06

Fe

0.16 ± 0.01

Si

3.16 ± 0.06

Ag

0.94 ± 0.04

P

0.25 ± 0.01

Sn

0.80 ± 0.03

S

0.18 ± 0.02

As

0.09 ± 0.02

Cl

7.37 ± 0.12

Pb

3.54 ± 0.05

K

0.37 ± 0.01

Cu

79.90 ± 0.27

Ca

0.91 ± 0.01

Tab.1: Results of a repeat measurement in the eye of the head. By using a small collimator size the XRF determination allows the analysis of just the eye on the coin, where 13 different elements were found. Cu is the dominating element, but light ones like Al or Si show a similar concentration as a heavy one like Pb.

In antiquity, coins were minted almost exclusively from metals and alloys like gold, electrum, silver, billon, potin and brass/orichalcum. If the alloy components and trace elements of a coin can be accurately determined, one can draw conclusions about its origin and age.

The powerful x-ray fluorescence measurement system FISCHERSCOPE® X-RAY XUV® is tailor-made for the analysis of alloys containing a broad spec-trum of elements. Together with the sophisticated evaluation software WinFTM®, it provides ideal conditions for such non-standard and challenging measurement tasks as determining the composition of antique coins. For further information please contact your local FISCHER representative.